If you've got a file cabinet or a bin for your documents that needs to be organized, file divider tabs are the way to go. File divider tabs are thin cardboard sheets that resemble half of a manila folder. When placed horizontally in a cabinet or bin, only the tab at the top of the divider will show. On the tab, write your organizing letter ("A") or group of letters ("A-G") and put all of the documents corresponding to those letters behind it.
A rolodex is essentially a miniature file cabinet, so alphabetical file dividers in rolodexes work in the same fashion as they do in file cabinets. If you're organizing phone numbers and/or addresses, create a tab for one letter or a group of letters, and place the phone numbers of anyone whose last name begins with that letter behind that tab.
An expanding file is usually what looks like a brown book, but when expanded, contains several dividers. Label the tabs in the expanding file for a letter or group of letters and organize your documents accordingly. Then, reseal the file, and your files will be in a safe, organized, compact place.
Every dictionary contains alphabetical dividers. Dictionary dividers usually don't actually separate pages, but instead are labeled on a small indent on the side of the page. And because dictionaries contain so much information, the labels are more specific, (i.e., rather than labeling each letter, a dictionary will label words beginning from Ba-Be, Be-Bl, and so on).